Why Did My DEXA Scan Say I Lost Muscle?

Updated October 23, 2026 · By the DEXASCAN.COM Team

Key takeaways

• DEXA "lean mass" includes muscle, organs, water and glycogen, not just muscle.
• Hydration and carbohydrate intake can shift lean mass by a kilogram or more in a day or two.
• Fat mass and bone readings are far less affected by those day-to-day swings.
• Scanning under the same conditions every time is the best way to see real change.
• DEXA, VO2 Max and RMR testing start at $89 on DEXASCAN.COM.

It's one of the most common posts in fitness and GLP-1 forums: "I've been lifting and eating more protein for three months, and my DEXA says I lost two pounds of muscle. What happened?" It's frustrating, especially on a GLP-1 medication. The good news: a single lower lean-mass number is often explained by water and fuel, not muscle. Here's how to tell the difference.

Did I really lose muscle, or is it water?

Often it's water. DEXA (dual-energy X-ray absorptiometry) is a low-dose X-ray scan that sorts your body into three compartments: fat mass, bone mineral and lean soft tissue. That last bucket is everything that isn't fat or bone, which means skeletal muscle plus organs, body water and the glycogen (stored carbohydrate) packed into your muscles and liver.

Because water and glycogen live inside "lean," anything that changes them changes your lean number, even if you haven't gained or lost a single muscle fiber. Common culprits include:

• A hard workout or sweaty session before your scan
• A low-carb or very low-calorie stretch, which drains glycogen (and the water stored with it)
• Not drinking much that morning, or drinking a lot more than usual
• Scanning at a different time of day than last time

If you're on a GLP-1 and eating much less than before, shifts in glycogen and water can be part of what you see. Our 2026 research roundup on GLP-1 muscle loss covers what the studies show about true lean-mass changes on these medications.

How much can hydration change a DEXA lean mass reading?

More than most people expect: studies have measured shifts of roughly 0.8 to 2.4 kilograms (about 2 to 5 pounds) within a day or two.

• A 2017 study in the European Journal of Applied Physiology had 12 active men cycle in a 30°C room until they lost 2.5% of their body weight. Afterward, DEXA showed their total lean tissue mass had dropped by an average of 1.69 kg. After 48 hours of rehydrating on a high-carbohydrate diet, lean mass rose by 2.36 kg. Fat mass and bone mineral didn't change at any point.
• A 2025 study in Frontiers in Physiology scanned 16 adults after a 12-hour fast, once with no fluids and once after drinking water equal to 1.5% of their body weight two hours before. Whole-body lean mass read 60.8 kg hydrated vs. 60.0 kg not hydrated, and trunk lean mass rose from 28.6 to 29.2 kg. Arm and leg lean mass did not change significantly.

Notice the extra water showed up in the trunk, not the limbs. That's why your arms-and-legs number is so useful for tracking real muscle.

Which DEXA number should I trust for muscle?

Look at your appendicular lean mass (arms plus legs) and your ALMI alongside total lean mass. ALMI, or appendicular lean mass index, is your arm and leg lean mass divided by your height squared. Most skeletal muscle is in your limbs, and limb readings were less affected by drinking water in the 2025 study above.

A quick self-check when your lean number drops:

1. Did fat mass drop too? In a calorie deficit, some lean loss alongside fat loss is expected.
2. Is the change mostly in the trunk? Trunk-only swings point toward water and gut contents.
3. Did your limbs hold steady? Stable arm and leg lean mass is a good sign your muscle is intact.
4. Were the conditions different? Time of day, food, fluids and training all count.

Our guide to ALMI and how it relates to healthy aging explains what a good number looks like, and you can learn more about visceral fat and ALMI on DEXASCAN.COM. If you want a line-by-line walkthrough of your report, see every number on your DEXA report, explained.

How do I get accurate DEXA results every time?

Keep your scan conditions the same. A 2016 study in the International Journal of Sport Nutrition and Exercise Metabolism compared a "best practice" protocol (scanned fasted and rested) with scans taken around random daily activity. The spread of lean-mass change scores was roughly double with the unstandardized scans (2–3%) compared with the standardized ones (1–2%), and the authors concluded DEXA scans should be done under the best-practice conditions.

Here's what that looks like in real life:

• Same time of day, ideally first thing in the morning
• Fasted, or at least the same pre-scan meal every time
• No workout before your scan; save training for afterward
• Similar fluid intake that morning, not a sudden extra liter
• Same clothing, with no metal, zippers or underwire
• Same location and machine, since different scanners and software can read slightly differently

What a DEXA scan shows, and what to do next

A whole-body DEXA scan takes about 10 minutes and shows your body fat percentage, lean muscle by region (each arm, leg and trunk), visceral fat (the deep fat around your organs) and bone density. That regional detail is exactly what lets you tell a water swing from a true change in muscle. See how DEXA body composition testing works for more.

If your last scan surprised you, here's a simple plan:

1. Don't panic over one scan. Compare limbs, trunk and fat mass before drawing conclusions.
2. Write down your scan conditions (time, food, fluids, training) so you can repeat them.
3. Keep lifting and eating enough protein; our data-driven guide to losing fat, not muscle walks through the basics.
4. Get a baseline scan under standardized conditions if you don't have one.
5. Rescan every 8–12 weeks at the same location, following the same routine each time.

Want a reason to stay consistent through the holidays? The National Body Composition Contest registration bundle pairs a challenge with your scans.

Frequently asked questions

Can dehydration make a DEXA scan show less muscle?

Yes. DEXA counts body water as part of lean mass, so being dehydrated can lower the reading. In a 2017 study in the European Journal of Applied Physiology, exercise dehydration reduced DEXA lean mass by an average of 1.69 kg in 12 active men, while fat mass and bone mineral stayed the same.

Does drinking water before a DEXA scan change the results?

It can change your total and trunk lean mass. A 2025 study in Frontiers in Physiology found whole-body lean mass read 60.8 kg after drinking water equal to 1.5% of body weight versus 60.0 kg without it, while arm and leg lean mass did not change significantly. Drink about the same amount before every scan.

How accurate is DEXA for tracking muscle changes?

DEXA tracks change most reliably when scans are done under the same conditions. A 2016 study in the International Journal of Sport Nutrition and Exercise Metabolism found the variability of lean-mass change scores was roughly half as large with fasted, rested scans as with scans taken around random daily activity. Consistency is what makes small changes meaningful.

How often should I get a DEXA scan to track muscle?

Most people rescan every 8 to 12 weeks, which gives enough time for real changes in muscle and fat to show up. Use the same location, time of day and pre-scan routine each time so you're comparing like with like.

How much does a DEXA scan cost?

Prices vary by provider and location. On DEXASCAN.COM, DEXA, VO2 Max and RMR testing start at $89, with prices shown upfront before you buy.

Related reading

• How often should you get a new DEXA scan?
• What's the most accurate way to measure body composition?
• Why the scale isn't moving (and what's really changing)

Find a DEXA scan near you

DEXASCAN.COM validates its providers and shows prices upfront, so you know what you're getting before you book. Buy your scan online and you'll get booking instructions within minutes. DEXA, VO2 Max and RMR testing start at $89, and scanning at the same location each time makes it easier to compare results.

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Sources: Toomey CM, McCormack WG, Jakeman P. The effect of hydration status on the measurement of lean tissue mass by dual-energy X-ray absorptiometry. European Journal of Applied Physiology, 2017; Influence of passive, diet-based, hydration on muscle quantity assessment. Frontiers in Physiology, 2025; Nana A, et al. Importance of standardized DXA protocol for assessing physique changes in athletes. International Journal of Sport Nutrition and Exercise Metabolism, 2016.

This article is for educational purposes and is not medical advice. Talk with your healthcare provider before starting or changing any medication, diet or exercise program.